Showing papers in "Geophysical Research Letters in 2021"

A Unified Clumped Isotope Thermometer Calibration (0.5–1,100°C) Using Carbonate-Based Standardization

Abstract: The potential for carbonate clumped isotope thermometry to independently constrain both the formation temperature of carbonate minerals and fluid oxygen isotope composition allows insight into long-standing questions in the Earth sciences, but remaining discrepancies between calibration schemes hamper interpretation of temperature measurements. To address discrepancies between calibrations, we designed and analyzed a sample suite (41 total samples) with broad applicability across the geosciences, with an exceptionally wide range of formation temperatures, precipitation methods, and mineralogies. We see no statistically significant offset between sample types, although the comparison of calcite and dolomite remains inconclusive. When data are reduced identically, the regression defined by this study is nearly identical to that defined by four previous calibration studies that used carbonate-based standardization; we combine these data to present a composite carbonate-standardized regression equation. Agreement across a wide range of temperature and sample types demonstrates a unified, broadly applicable clumped isotope thermometer calibration.

Differing Mechanisms of New Particle Formation at Two Arctic Sites

Abstract: New particle formation in the Arctic atmosphere is an important source of aerosol particles. Understanding the processes of Arctic secondary aerosol formation is crucial due to their significant impact on cloud properties and therefore Arctic amplification. We observed the molecular formation of new particles from low-volatility vapors at two Arctic sites with differing surroundings. In Svalbard, sulfuric acid (SA) and methane sulfonic acid (MSA) contribute to the formation of secondary aerosol and to some extent to cloud condensation nuclei (CCN). This occurs via ion-induced nucleation of SA and NH 3 and subsequent growth by mainly SA and MSA condensation during springtime and highly oxygenated organic molecules during summertime. By contrast, in an ice-covered region around Villum, we observed new particle formation driven by iodic acid but its concentration was insufficient to grow nucleated particles to CCN sizes. Our results provide new insight about sources and precursors of Arctic secondary aerosol particles. Plain Language Summary Cloud properties are sensitive to the formation of new aerosol particles in the Arctic atmosphere, yet little is known about the chemistry and processes controlling this phenomenon. Here, based on comprehensive in situ measurements, we identify the very first steps of atmospheric new particle formation, that is, formation of small clusters from compounds present in the gas phase, and candidates for the subsequent growth of these clusters to larger sizes, at two Arctic sites: one surrounded by open waters, the other one by sea ice. We show how environmental differences affect secondary aerosol formation via emissions and atmospheric chemistry of aerosol precursor gases. Our results provide previously unidentified insight into how future changes in the Polar environment could BECK ET AL.

Warming and Freshening of the Pacific Inflow to the Arctic From 1990 2019 Implying Dramatic Shoaling in Pacific Winter Water Ventilation of the Arctic Water Column

Abstract: The Pacific inflow to the Arctic traditionally brings heat in summer, melting sea ice; dense waters in winter, refreshing the Arctic’s cold halocline; and nutrients in all seasons, supporting Arctic ecosystems. Year-round Bering Strait moorings from 1990-2019 find increasing (0.010±0.006Sv/yr) northward flow, reducing Chukchi Sea residence times from ~7.5 to ~4.5 months. Annual mean temperatures show significant warming (0.05±0.02°C/yr), with faster change (~0.1°C/yr) in warming (June) and cooling (October/November) months, which are now 2-4°C above climatology. Warm water duration increased from 5.5 months (1990s) to over 7 months (2017), mostly due to earlier warming (1.3±0.7days/yr). Dramatic winter-only (JanuaryMarch) freshening (0.03psu/yr), makes winter waters fresher than summer waters. The resultant density change in winter, too large to be compensated by Chukchi Sea sea-ice processes, shoals the Pacific Winter Water equilibrium depth in the Arctic from 100-150m to 50-100m, implying Pacific Winter Water no longer ventilates the Arctic’s cold halocline at 33.1psu. Plain Language Summary The Bering Strait is the only oceanic link between the Pacific and the Arctic Oceans. The typically northward flow through the strait carries Pacific oceanic nutrients to the Arctic, vital for ecosystems. The flow varies seasonally in temperature and salinity. In spring/summer, it brings warm waters that start the melt-back of Arctic sea ice. In winter, it carries cold waters that traditionally sink deeper (100-150m) into the Arctic, well below the summer waters. Annuallyserviced instrumentation moored to the sea floor almost continuously have measured (hourly) the water flow and properties in the strait from autumn 1990 to summer 2019. We find the flow is increasing significantly, almost halving the time taken to reach the Arctic from the strait. Now, summer waters are 2-4°C warmer than typical in the 1990s and warm for longer (7 months compared to 5.5 months). In winter, waters are dramatically fresher than before, now fresher than in summer. This change means the winter waters can no longer sink so deep in the Arctic now only 50-100m, the same depth as the summer waters. This not only means oceanic nutrients are available closer to the surface, but may also restructure how the upper Arctic Ocean mixes.

COVID-19 Crisis Reduces Free Tropospheric Ozone across the Northern Hemisphere

Abstract: Throughout spring and summer 2020, ozone stations in the northern extratropics recorded unusually low ozone in the free troposphere. From April to August, and from 1 to 8 kilometers altitude, ozone was on average 7% (≈4 nmol/mol) below the 2000 to 2020 climatological mean. Such low ozone, over several months, and at so many stations, has not been observed in any previous year since at least 2000. Atmospheric composition analyses from the Copernicus Atmosphere Monitoring Service and simulations from the NASA GMI model indicate that the large 2020 springtime ozone depletion in the Arctic stratosphere contributed less than one quarter of the observed tropospheric anomaly. The observed anomaly is consistent with recent chemistry‐climate model simulations, which assume emissions reductions similar to those caused by the COVID‐19 crisis. COVID‐19 related emissions reductions appear to be the major cause for the observed reduced free tropospheric ozone in 2020.

Five Decades of Observed Daily Precipitation Reveal Longer and More Variable Drought Events Across Much of the Western United States

Abstract: Understanding the impacts of climate change on the hydrologic cycle of the western United States (US) remains an area of critical uncertainty, though emerging evidence suggests precipitation deficits will be amplified by climate warming, with severe consequences for vegetation, water supplies, agriculture, wildlife, and wildfire risk (Cook et al, 2014, 2020; Dai, 2011, 2013; Mankin et al., 2017; Maurer et al., 2020; Milly & Dunne, 2020; Parks et al., 2016). Although the total amount of precipitation is a key commonly reported metric, often the temporal consistency of precipitation is more important than the total amount for maintaining adequate soil moisture supply, forage for livestock and wildlife, the replenishment of human water resources, and the mitigation of wildfire risk (Heisler-White et al., 2008; Littell et al., 2016; Liu et al., 2010). Thus, the timing and duration of dry interval (time between precipitation events) is fundamental to Abstract Multiple lines of evidence suggest climate change will result in increased precipitation variability and consequently more frequent extreme events. These hydroclimatic changes will likely have significant socioecological impacts, especially across water-limited regions. Here we present an analysis of daily meteorological observations from 1976 to 2019 at 337 long-term weather stations distributed across the western United States (US). In addition to widespread warming (0.2 °C ± 0.01°C/decade, daily maximum temperature), we observed trends of reduced annual precipitation (−2.3 ± 1.5 mm/ decade) across most of the region, with increasing interannual variability of precipitation. Critically, daily observations showed that extreme-duration drought became more common, with increases in both the mean and longest dry interval between precipitation events (0.6 ± 0.2, 2.4 ± 0.3 days/decade) and greater interannual variability in these dry intervals. These findings indicate that, against a backdrop of warming and drying, large regions of the western US are experiencing intensification of precipitation variability, with likely detrimental consequences for essential ecosystem services.

Distributed Global Debris Thickness Estimates Reveal Debris Significantly Impacts Glacier Mass Balance.

Abstract: Supraglacial debris affects glacier mass balance as a thin layer enhances surface melting, while a thick layer reduces it. While many glaciers are debris-covered, global glacier models do not account for debris because its thickness is unknown. We provide the first globally distributed debris thickness estimates using a novel approach combining sub-debris melt and surface temperature inversion methods. Results are evaluated against observations from 22 glaciers. We find the median global debris thickness is ∼0.15 ± 0.06 m. In all regions, the net effect of accounting for debris is a reduction in sub-debris melt, on average, by 37%, which can impact regional mass balance by up to 0.40 m water equivalent (w.e.) yr-1. We also find recent observations of similar thinning rates over debris-covered and clean ice glacier tongues is primarily due to differences in ice dynamics. Our results demonstrate the importance of accounting for debris in glacier modeling efforts.

Space-Borne Cloud-Native Satellite-Derived Bathymetry (SDB) Models Using ICESat-2 And Sentinel-2

Abstract: Shallow nearshore coastal waters provide a wealth of societal, economic and ecosystem services, yet their topographic structure is poorly mapped due to a reliance upon expensive and time intensive ...

Global changes in 20‐year, 50‐year, and 100‐year river floods

Abstract: Concepts like the 100-year flood event can be misleading if they are not updated to reflect significant changes over time. Here, we model observed annual maximum daily streamflow using a nonstationary approach to provide the first global picture of changes in: (a) the magnitudes of the 20-, 50-, and 100-year floods (i.e., flows of a given exceedance probability in each year); (b) the return periods of the 20-, 50-, and 100-year floods, as assessed in 1970 (i.e., flows of a fixed magnitude); and (c) corresponding flood probabilities. Empirically, we find the 20-/50-year floods have mostly increased in temperate climate zones, but decreased in arid, tropical, polar, and cold zones. In contrast, 100-year floods have mostly decreased in arid/temperate zones and exhibit mixed trends in cold zones, but results are influenced by the small number of stations with long records, and highlight the need for continued updating of hazard assessments.

Changing Lengths of the Four Seasons by Global Warming

Abstract: How long will the four seasons be by 2100? Increasing evidence suggests that the length of a single season or in regional scales has changed under global warming, but a hemispherical-scale response of the four seasons in the past and future remains unknown. We find that summer in the Northern Hemisphere midlatitudes has lengthened, whereas winter has shortened, owing to shifts in their onsets and withdrawals, accompanied by shorter spring and autumn. Such changes in lengths and onsets can be mainly attributed to greenhouse-warming. Even if the current warming rate does not accelerate, changes in seasons will still be exacerbated in the future. Under the business-as-usual scenario, summer is projected to last nearly half a year, but winter less than 2 months by 2100. The changing seasonal clock signifies disturbed agriculture seasons and rhythm of species activities, more frequent heat waves, storms and wildfires, amounting to increased risks to humanity. Plain Language Summary A series of phenomena such as early flowering of plants and early migratory birds are suggesting that the traditional four seasons may have changed. We focus on how the four seasons changed during 1952-2011 and will change by the end of this century in the warming Northern Hemisphere midlatitudes. We find that lengths and start dates of the four seasons have changed, and the changes will be amplified in the future. Over the period of 1952-2011, the length of summer increased from 78 to 95 days and that of spring, autumn and winter decreased from 124 to 115,87 to 82, and 76 to 73 days, respectively. In addition, summer is projected to last nearly half a year, but winter less than 2 months by 2100. Such changes can trigger a chain of reactions in agriculture, policy-making for agricultural management and disaster prevention requires adjustment accordingly. The seasonal-related topics involving ecology, the ocean and the atmosphere also need to be revisited.

Chemistry of Atmospheric Fine Particles During the COVID-19 Pandemic in a Megacity of Eastern China

Abstract: Air pollution in megacities represents one of the greatest environmental challenges Our observed results show that the dramatic NOx decrease (77%) led to significant O3 increases (a factor of 2) during the COVID-19 lockdown in megacity Hangzhou, China Model simulations further demonstrate large increases of daytime OH and HO2 radicals and nighttime NO3 radical, which can promote the gas-phase reaction and nocturnal multiphase chemistry Therefore, enhanced NO3− and SO42− formation was observed during the COVID-19 lockdown because of the enhanced oxidizing capacity The PM2 5 decrease was only partially offset by enhanced aerosol formation with its reduction reaching 50% In particular, NO3− decreased largely by 68% PM2 5 chemical analysis reveals that vehicular emissions mainly contributed to PM2 5 under normal conditions in Hangzhou Whereas, stationary sources dominated the residual PM2 5 during the COVID-19 lockdown This study provides evidence that large reductions in vehicular emissions can effectively mitigate air pollution in megacities © 2020 The Authors

Climate Impacts of COVID-19 Induced Emission Changes

Abstract: The COVID-19 pandemic led to dramatic changes in economic activity in 2020 We use estimates of emissions changes for 2020 in two Earth System Models (ESMs) to simulate the impacts of the COVID-19 economic changes Ensembles of nudged simulations are used to separate small signals from meteorological variability Reductions in aerosol and precursor emissions, chiefly Black Carbon (BC) and sulfate (SO4), led to reductions in total anthropogenic aerosol cooling through aerosol-cloud interactions The average overall Effective Radiative Forcing (ERF) peaks at +0 29±0 15 Wm?2 in spring 2020 Changes in cloud properties are smaller than observed changes during 2020 Impacts of these changes on regional land surface temperature range up to +0 3K The peak impact of these aerosol changes on global surface temperature is very small (+0 03K) However, the aerosol changes are the largest contribution to radiative forcing and temperature changes as a result of COVID-19 affected emissions, larger than ozone, CO2 and contrail effects

Increasing Synchronous Fire Danger in Forests of the Western United States

Abstract: Author(s): Abatzoglou, John T; Juang, Caroline S; Williams, A Park; Kolden, Crystal A; Westerling, Anthony LeRoy

The Synergistic Role of Sulfuric Acid, Bases, and Oxidized Organics Governing New-Particle Formation in Beijing

Abstract: Intense and frequent new particle formation (NPF) events have been observed in polluted urban environments, yet the dominant mechanisms are still under debate. To understand the key species and governing processes of NPF in polluted urban environments, we conducted comprehensive measurements in downtown Beijing during January–March, 2018. We performed detailed analyses on sulfuric acid cluster composition and budget, as well as the chemical and physical properties of oxidized organic molecules (OOMs). Our results demonstrate that the fast clustering of sulfuric acid (H2SO4) and base molecules triggered the NPF events, and OOMs further helped grow the newly formed particles toward climateand health-relevant sizes. This synergistic role of H2SO4, base species, and OOMs in NPF is likely representative of polluted urban environments where abundant H2SO4 and base species usually co-exist, and OOMs are with moderately low volatility when produced under high NOx concentrations. Plain Language Summary Atmospheric new particle formation (NPF) is a dominant source of atmospheric ultrafine particles worldwide. Those particles profoundly influence climate and human health. NPF includes two consecutive processes, that is, the formation of new particles (∼2 nm in diameter) and their subsequent growth to larger sizes. Extensive studies conducted in the laboratory and in forested areas have shown that many gaseous species can participate in NPF, such as sulfuric acid, ammonia, amines, and oxidize organic molecules. However, the actual roles of these vapors may vary significantly from location to location and are largely unclear in urban environments. Here, based on measurements of sulfuric acid, sulfuric acid clusters, and oxidize organic molecules, we demonstrate that sulfuric acid and base molecules were responsible for the initial formation of new particles during a wintertime field campaign in Beijing. The majority of oxidized organic molecules had a minor YAN ET AL. © 2021. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. The Synergistic Role of Sulfuric Acid, Bases, and Oxidized Organics Governing New-Particle Formation in Beijing Chao Yan , Rujing Yin, Yiqun Lu , Lubna Dada , Dongsen Yang, Yueyun Fu, Jenni Kontkanen , Chenjuan Deng, Olga Garmash , Jiaxin Ruan, Rima Baalbaki , Meredith Schervish, Runlong Cai, Matthew Bloss, Tommy Chan , Tianzeng Chen , Qi Chen, Xuemeng Chen, Yan Chen, Biwu Chu, Kaspar Dällenbach, Benjamin Foreback, Xucheng He, Liine Heikkinen , Tuija Jokinen, Heikki Junninen, Juha Kangasluoma , Tom Kokkonen , Mona Kurppa, Katrianne Lehtipalo , Haiyan Li, Hui Li , Xiaoxiao Li, Yiliang Liu, Qingxin Ma , Pauli Paasonen , Pekka Rantala , Rosaria E. Pileci , Anton Rusanen, Nina Sarnela , Pauli Simonen , Shixian Wang, Weigang Wang , Yonghong Wang , Mo Xue, Gan Yang, Lei Yao, Ying Zhou, Joni Kujansuu, Tuukka Petäjä, Wei Nie , Yan Ma, Maofa Ge , Hong He, Neil M. Donahue , Douglas R. Worsnop, Veli-Matti Kerminen, Lin Wang , Yongchun Liu, Jun Zheng , Markku Kulmala , Jingkun Jiang , and Federico Bianchi Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Aerosol and Haze Laboratory, Beijing University of Chemical Technology, Beijing, China, Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, Helsinki, Finland, School of Environment, State Key Joint Laboratory of Environment Simulation and Pollution Control, Tsinghua University, Beijing, China, Department of Environmental Science & Engineering, Fudan University, Shanghai, China, Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, Nanjing University of Information Science & Technology, Nanjing, China, Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA, USA, Research Center for EcoEnvironmental Sciences, Chinese Academy of Science, Beijing, China, School of Environmental Sciences, Peking University, Beijing, China, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China, Laboratory of Environmental Physics, Institute of Physics, University of Tartu, Tartu, Estonia, Finnish Meteorological Institute, Helsinki, Finland, Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), Villigen, Switzerland, Aerosol Physics Laboratory, Physics Unit, Tampere University, Tampere, Finland, School of Atmospheric Sciences, Joint International Research Laboratory of Atmospheric and Earth System Sciences, Nanjing University, Nanjing, China, Aerodyne Research Inc., Billerica, MA, USA Key Points: • Process-level understanding of new particle formation (NPF) in wintertime Beijing was obtained based on measurement state-of-theart instruments • The analysis of sulfuric acid cluster composition and budget showed that sulfuric acid-base clustering initiated NPF • Condensable organic vapors were characterized and demonstrated to have a crucial influence on the growth of newly formed particles Supporting Information: Supporting Information may be found in the online version of this article.

Historical and projected changes in the Southern Hemisphere surface westerlies

Abstract: Changes to the Southern Hemisphere (SH) surface westerlies not only affect air temperature, storm tracks and precipitation; they are also pivotal in controlling global ocean circulation, ocean heat...

Subseasonal Forecasts of Opportunity Identified by an Explainable Neural Network

Abstract: Midlatitude prediction on subseasonal timescales is difficult due to the chaotic nature of the atmosphere and often requires the identification of favorable atmospheric conditions that may lead to ...

Surface Melt and Runoff on Antarctic Ice Shelves at 1.5°C, 2°C, and 4°C of Future Warming

Abstract: The future surface mass balance (SMB) of Antarctic ice shelves has not been constrained with models of sufficient resolution and complexity. Here, we force the high‐resolution Modele Atmospherique Regional (MAR) with future simulations from four CMIP models to evaluate the likely effects on the SMB of warming of 1.5°C, 2°C and 4°C above pre‐industrial temperatures. We find non‐linear growth in melt and runoff which causes SMB to become less positive with more pronounced warming. Consequently, Antarctic ice shelves may be more likely to contribute indirectly to sea level rise via hydrofracturing‐induced collapse, which facilitates accelerated glacial discharge. Using runoff and melt as indicators of ice shelf stability, we find that several Antarctic ice shelves (Larsen C, Wilkins, Pine Island and Shackleton) are vulnerable to disintegration at 4°C. Limiting 21st century warming to 2°C will halve the ice shelf area susceptible to hydrofracturing‐induced collapse compared to 4°C.

New Precise Dating of the India‐Asia Collision in the Tibetan Himalaya at 61 Ma

Abstract: The India-Asia collision induced rapid uplift of the Tibetan Plateau and affected global atmospheric and oceanic circulation through the Cenozoic (Z. An et al., 2001; Ravizza & Zachos, 2014). Geological records both in the western (Indus suture zone) and central-eastern Himalaya (Yarlung-Zangbo suture zone; YZSZ) indicate an early Paleogene collision event, interpreted as India colliding with either an intra-oceanic arc (e.g., Aitchison et al., 2007) or with Asia (e.g., Garzanti, 2008). Because no record of an oceanic basin still open after this collision event has ever been documented either in the central Himalaya to the south or in Tibet to the north, the latter hypothesis (DeCelles et al., 2014; Hu et al., 2016) is favored here.

Venus' Mass Spectra Show Signs of Disequilibria in the Middle Clouds

Abstract: We present a re-examination of mass spectral data obtained from the Pioneer Venus Large Probe Neutral Mass Spectrometer. Our interpretations of differing trace chemical species are suggestive of re...